Hospital-induced delirium is an often ignored or underdiagnosed illness affecting a large number of senior patients.
The condition is a temporary form of cognitive impairment that can last anywhere between a few days and a few weeks. It is believed to be caused by the changes that come with hospitalization, isolation, and overmedication.
Up to a third of patients over the age of 70 experience delirium, and those having surgery or in the intensive care unit are affected at a higher rate.
Until recently, the condition had been considered normal and simply put down to old age. More and more research, however, is showing that although common, the condition is not normal. It can have negative long-term cognitive effects and can sometimes lead to complications, such as blood clots or pneumonia.
Researchers from University College London (UCL) and the University of Cambridge, both in the United Kingdom, set out to investigate whether there was a link between post-delirium cognitive decline and the pathologic progress of dementia.
The scientists were led by Dr. Daniel Davis, from the MRC Unit for Lifelong Health and Aging at UCL, and the findings were published in the journal JAMA Psychiatry.
Examining the link between delirium and dementia
Davis and team examined the brains and cognitive abilities of 987 brain donors from three population-based studies in Finland and the U.K. The participants were aged 65 years and over.
The study included neuropathologic evaluations performed by investigators who were blinded to the clinical data.
Before death, the brain donors were followed up for an average of 5.2 years, during which time the researchers recorded each individual's experience of delirium using interviews.
They assessed the participants' cognitive abilities and cognitive decline by using the Mini-Mental State Examination score.
After death, researchers performed brain autopsies to look for neuropathologic dementia markers - such as neurofibrillary tangles and neocortical amyloid plaques, as well as vascular and Lewy body pathologic features - in the brain's substantia nigra.
Of the 987 participants, 279 (28 percent) had a history of delirium.
The researchers then examined the rate of cognitive decline and how it interacted with the dementia and delirium pathologic burden.
Treating delirium may 'delay or reduce' dementia
Overall, the slowest decline was observed in individuals with no history of delirium and the lowest dementia pathologic burden, while the fastest cognitive decline was seen in those with both delirium and dementia burden.
Interestingly, both delirium and dementia neuropathologic features taken together were associated with a much higher rate of cognitive decline than what is typically expected for delirium or dementia-related neuropathologic processes taken individually.
As the authors explain, "this means that delirium may be independently associated with pathologic processes that drive cognitive decline, which are different from the pathologic processes of classic dementia."
Although more research is needed to explain exactly how delirium may cause dementia, Dr. Davis emphasizes the importance of the study and its consequences on how we understand and treat this form of temporary mental impairment.
"Unfortunately, most delirium goes unrecognized. In busy hospitals, a sudden change in confusion [may] not be noticed by hospital staff [as] patients can be transferred several times and staff often switch over [...]. If delirium is causing brain injury in the short- and long-term, then we must increase our efforts to diagnose, prevent and treat delirium. Ultimately, targeting delirium could be a chance to delay or reduce dementia."
Association of delirium with cognitive decline in late life: A neuropathologic study of 3 population-based cohort studies, Daniel H. J. Davis et al., JAMA Psychiatry, doi:10.1001/jamapsychiatry.2016.3423, published online 18 January 2017.
UCL news release, accessed 18 January 2017 via Newswise.
Additional source: Hospital-induced delirium hits hard, Roger Collier, CMAJ JAMC, doi:10.1503/cmaj.109-4069, published online 10 January 2012.